In the formation of photosensitive silver halide emulsions, the ripening or growing step during which time the silver halide grains grow is considered important. During the ripening stage an adequate concentration of a silver halide solvent, for example, excess halide, generally bromide, is employed which renders the silver halide much more soluble than it is in pure water because of the formation of complex ions. This facilitates the growth of the silver halide grains. While excess bromide and ammonia are the most common ripening agents, the literature also mentions the use of water-soluble thiocyanate compounds in place of bromide as well as a variety of amines. See, for example, Photographic Emulsion Chemistry, G. F. Duffin, The Focal Press, London, 1966, page 59.
With respect to ammonia as a ripening agent, The Theory of the Photographic Process, T. H. James, Fourth Edition, MacMillan Publishing Co., Inc. New York, 1977, on page 89, states:
"On the basis of the mode of precipitation, there are two classes of emulsions: neutral or acid emulsions and ammoniacal emulsions. In the first class, alkali halide is dissolved in water containing the peptizing gelatin, and to this solution is added, under controlled conditions, the desired amount of silver nitrate solution; or the alkali halide and silver nitrate solutions are added simultaneously to the gelatin solution. A large excess of alkali halide may be used to promote physical ripening, and such ripening is increased by higher temperature and longer time of action. Ammoniacal emulsions are prepared by adding ammonium hydroxide during precipitation and/or ripening. Ammonia, because of its solvent action, accelerates physical ripening. The ammonia may be added to the halide solution or the silver nitrate solution may be converted by ammonium hydroxide to the silver/ammonia complex, which is then added to the halide solution. Upon reaction with halide, ammonia is released and the silver halide is precipitated and undergoes ripening."
Copending application of Edwin H. Land, Ser. No. 234,937, filed Feb. 17, 1981, (common assignee) is directed to a method for forming a predetermined spaced array of sites and then forming single effective silver halide grains at said sites. Thus, by forming the sites in a predetermined spatial relationship, if the silver halide grains are formed only at the sites, each of the grains will also be located at a predetermined and substantially uniform distance from the next adjacent grain and their geometric layout will conform to the original configuration of the sites.
The term, "single effective silver halide grain", refers to an entity at each site which functions photographically as a single unit which may or may not be crystallographically a single crystal but one in which the entire unit can participate in electronic and ionic processes such as latent image formation and development.
Copending application Ser. No. 234,937 discloses one method for forming sites by exposing a photosensitive material to radiation actinic to said photosensitive material and developing the so-exposed photosensitive material to provide sites for the generation of silver halide corresponding to the pattern of exposure and then forming photosensitive silver halide grains at the sites. In a preferred embodiment, the sites are provided by the predetermined patterned exposure of the photoresist whereby upon development of an exposed photoresist a relief pattern is obtained wherein the peaks or valleys comprise the above described sites.
Preferably, the photoresist is exposed by interfering coherent radiation in order to provide sites with a desired spacing therebetween. Thus, exposure of the photoresist can be carried out by two interfering coherent beams wherein the beams providing the exposures are at an angle to each other. The intersection of maximum intensities of the two combined exposures will provide a greater degree of modifications to the photoresist at the points of intersection than the remainder of the photosensitive material.
Preferably, the source of coherent radiation is a laser. The particular laser will be selected depending upon the absorption spectrum and spectral response characteristics of the specific photoresist employed.
Subsequent to exposure of the photoresist, the relief pattern is formed by developing the exposed photoresist. For example, employing a photoresist wherein solubilization is achieved by exposure, development of the exposed photoresist would result in the removal of selected areas to provide a relief pattern consisting of regular depressions or holes in the photoresist. As disclosed in copending application Ser. No. 234,937, a variety of specific relief configurations can be obtained depending upon the specific material employed and the exposure and developing conditions selected. Copending application of James J. Cowan, Arthur M. Gerber and Warren D. Slafer, Ser. No. 234,959 filed, Feb. 17, 1981 also discloses and claims methods for producing specific relief patterns.
While the single effective silver halide grains may be formed employing the described photoresist relief pattern, it is preferred to replicate the relief pattern by conventional means, for example, by using conventional electroforming techniques to form an embossing master from the original relief image and using the embossing master to replicate the developed photoresist pattern in an embossable polymeric material.
Having produced the described relief pattern, silver halide grains are then formed by a variety of disclosed procedures at the specific sites.
Copending application of Arthur M. Gerber, Ser. No. 298,640, filed concurrently herewith (common assignee), discloses and claims the formation of single effective grains in a predetermined spaced array by coalescing fine-grain silver halide in a plurality of predetermined spaced depressions in a surface. A preferred method of coalescence comprises contacting the fine-grain emulsion with a solution of a silver halide solvent.
By means of the present invention, a novel method for forming a predetermined spaced array of silver halide grains in a relief pattern has been found.